1. Field of the Invention
This invention relates generally to focusing devices and more particularly to a focuser for an optical instrument.
2. Prior Art
Devices for focusing optical instruments have been known and in use for many years.
A first typical focusing mount is disclosed in U.S. Pat. No. 3,051,045. This mount comprises an eyepiece having an inner end threadedly carried in an opening in a housing attached to a telescope. In a top part of the mount is a passageway. In respective ends of the mount passageway are bushings that hold ends of a shaft. On the shaft between the bushings is a pinion gear operatively engaging external threads on the eyepiece. Coarse focus adjustment is obtained by rotating knobs on respective shaft ends. Rotation of the eyepiece then produces fine focus adjustment.
Further focusing apparatus particularly adapted for a slide projector is disclosed in U.S. Pat. No. 3,060,767. This apparatus includes a cylindrical lens tube slidably carried in a V-shaped tough attached to a base of the projector. Longitudinal movement of the lens tube is guided in part by a pair of upper, transversely spaced apart, beveled-edged rollers. These upper guide rollers are spring biased to compressively engage an upper side of the tube and press the tube against a lower tough. Additionally, longitudinal tube movement is controlled by a set of lower, spaced apart, rubber coated, guide rollers. These lower rollers extend upwardly through openings in the trough to operatively engage a lower side of the tube.
A recently developed camera lens zooming device then is set out in U.S. Pat. No. 5,162,948. This device includes an outer barrel having an inner, cylindrical-shaped opening. In a sidewall of this opening is a pair of aligned, longitudinally spaced apart grooves. Then, spaced radially about 120 degrees apart on respective sides of these grooves are an inward extending, longitudinal flange and a slot. A spring element having a top groove is positioned in the slot while the flange has a side groove. Slidably disposed in the barrel is a cylindrical mount element. In an outer sidewall of the mount element is a further pair of aligned, longitudinally spaced apart grooves. Then, spaced radially about 120 degrees on one side of these grooves is an outward extending, longitudinal flange. The position of the mount element is maintained in the barrel by ball bearings in the grooves, a ball bearing in the spring slot, and a ball bearing in the flange slot. The spring bearing presses against the mount element while the flange bearing interfaces between the two flanges.
A most recent focuser for adjusting the position of an eyepiece of an optical instrument is disclosed in U.S. Pat. No. 5,303,090. This focuser includes a mounting base having a cylindrical-shaped inner passageway for placement of a drawtube. The drawtube is secured in the passageway in part by two pairs of radially spaced apart roller bearings. The bearings of each pair are longitudinally aligned and rotatively carried between upstanding elements on an upper portion of the base. A bottom segment of each bearing extends through an opening in the base to engage an outer side of the drawtube. Extending from a bottom portion of the base is a pair of spaced apart, slotted mounts fitted with carriage elements that hold respective ends a control shaft. This shaft extends tangentially through the base passageway to fictionally engage a tread area on the drawtube outer side. Frictional loading is controlled by jack screws that press against the shaft ends. During use, knobs on ends of the control shaft are selectively turned to effect shaft rotation that moves the drawtube and attached eyepiece to a focused position.